Spring charging means and linkage mechanism for preventing contact rebound in switches

ABSTRACT

An electro-magnet operated switch is actuated through a nonlinear motion transmission in &#39;&#39;&#39;&#39;high-gear&#39;&#39;&#39;&#39; while moving through the gap and in &#39;&#39;&#39;&#39;low gear&#39;&#39;&#39;&#39; when the contacts engage. A large amount of contact pressure is applied when the contacts engage by a preloaded spring pressed roller, this being made possible by the mechanical advantage given the electro-magnet plunger at this time. The connection of the movable contact with its operator is solid and non-yielding. The combined action of low speed contact engagement, heavy contact pressure and non-yielding connection resists or eliminates contact bounce. In effect, the mechanism closes the contact gap against no force and then rolls on an already existing force to supply the contact pressure. This reduces the power required and makes it possible to use a smaller electro-magnet.

United States Patent [191 Harris SPRING CHARGING MEANS AND LINKAGE MECHANISM FOR PREVENTING CONTACT REBOUND IN SWITCHES [75] Inventor: John L. Harris, Delafield, Wis. [73] Assignee: Deltrol Corp., Bellwood, Ill.

[22] Filed: Oct. 26, 1971 211 Appl. No.: 192,533

[52] US. Cl 200/153 SC, 200/166 H, 335/190 [51] Int. Cl. H0lh 3/32 [58] Field of Search..... 200/16 A, 153 LB, 153 LA, 200/166 H, 153 L, 170 A, 170 R, 163;

Lindsay 335/190 [451 Apr. 30, 1974 2,523,774 9/1950 Moran 335/190 Primary Examiner.la.mes R. Scott [57] ABSTRACT An electro-magnet operated switch is actuated through a non-linear motion transmission in highgear while moving through the gapand in low gear when the contacts engage. A large amount of contact pressure is applied when the contacts engage by a preloaded spring pressed roller, this being made possible by the mechanical advantage given the electro-magnet plunger at this time. The connection of the movable contact with its operator is solid and non-yielding. The combined action of low speed contact engagement, heavy contact pressure and non-yielding connection resists or eliminates contact bounce. in effect, the mechanism closes the contact gap against no force and then rolls on an already existing force to supply the contact pressure. This reduces the power required and makes it possible to use a smaller electro-magnet.

18 Claims, 7 Drawing Figures :aQsoslsav PATENTEDAPR30 m4 SHEET) 2 UF 2 MENTOR. A 4%,;

1 SPRINGCI-IARGING MEANS AND LINKAGE MECHANISM FOR PREVENTING CONTACT REBOUND IN SWITCHES BACKGROUND OF THE INVENTION This invention relates to electric switches.

In medium duty electro-magnetic switches two stationary contacts are bridged by a movable contact bar. The contact bar is carried by a slide actuated by the plunger of an electro-magnet. Energization of the electro-magnet moves the contact bar into engagement against the action of a return spring. Deenergization of the electro-magnet allows the return spring to move the slide and plunger for disengaging the contacts and moving the contact bar through a gap to the open position.

In order to allow the plunger to seat after the contacts close and to compensate for manufacturing tolerances, the contact bar is loosely mounted on the slide on a track allowing substantial movement of the slide after the contacts close. An overtravel spring is provided between the contact bar and the slide urging the contact bar into engagement with the stationary contacts. This spring is preloaded in the slide and serves to provide a minimum contact pressure when the contacts engage.

With this prior art arrangement, the return spring for opening the contacts must have sufficient strength to do so even if welding takes place. This requires the electro-magnet to develop sufficient force to hold this spring in stretch position. In addition, on the closing stroke after the bridging bar engages the stationary contacts, the force of the overtravel spring must be opposed by the electro-magnet, and this force builds up as the electro-magnet completes its stroke. Thus, the electro-magnet when seated must directly oppose the combined forces of the return spring and overtravel spring.

Another disadvantage of the prior art construction is that it is prone to allow contact bounce to occur when the contacts engage. This is permitted by the overtravel spring which is the only thing opposing the hammer ac tion bouncing force. Bouncing can be reduced by making the overtravel spring stronger but this requires more pull by the electro-magnet which increases the hammer action causing the bounce.

BRIEF SUMMARY OF INVENTION The primary object of the invention is to provide a more efficient switch operating mechanism, thus reducing the size and cost of the mechanism supplying the power for operating a switch.

Applicants invention makes use of the well known physics principle that work done is the product of force x distance. If the switch contacts are moved through the contact gap against no force, no work is required. If the contact pressure is applied without moving anything through any distance, no work is required. With a perfect operating mechanism, a movable-contact of a switch could be moved through an infinite distance and closed with infinite contact pressure without requiring any power.

Another object of the invention is to reduce or eliminate contact bounce.

In applicants invention, the slide carrying the movable contact bar is operated by an electro-magnet through a non-linear motion transmission means. In one form it consists of a roller moved laterally by the electro-magnet and riding on camming surfaces on the slide. This roller rides on a track determining its path and is pressed in contact engaging direction by a preloaded spring which supplies the contact pressure when the contacts engage. The contact bar instead of being actuated by the slide through an overtravel spring is attached to the slide in a non-yielding manner.

In operation, when the electro-magnet is energized, it moves the slide in high gear" through the contact gap. At this time very little force is required as the only resistance is friction and a slight movement of the electro-magnet plunger can give a large travel of the plunger through the air gap.

As the contacts approach engagement, the camming angle changes giving less travel of the slide per increment of movement of the plunger. When the contacts engage, the roller continues traveling on the reduced slope of the camming surface and separates from its track. The pressure of the roller spring now applies contact pressure to thecontacts. Due to the slowing down of the contact engaging speed by the non-linear motion. transmission, and the non-yielding connection between the contact bar and slide, contact bounce is eliminated or greatly reduced. Due to the non-linear action, the electro-magnet gives maximum motion when little force is required and maximum pressure when little movement is required. This makes it possible for the electro-magnet to be considerably smaller and less expensive than in prior art devices.

Other and more specific objects of the invention will appear from the following detailed description and appended claims.

- FIG. 1 is an elevation partly in section of an electromagnet operated switch embodying the invention.

FIG. 2 is an end view looking fromthe left ,hand end of FIG. 1.

FIG. 3 is a sectional view taken on line 3-3 of FIG.

FIG. 4 is a top view of the roller and solenoid yoke assembly.

FIG. 5 is a side view of FIG. 4.

FIG. 6 is a front view partly in section of a modified form of the invention.

FIG. 7 is a fragmentary view showing the positions of the working parts assumed when the contacts are closed.

. DETAILED DESCRIPTION OF INVENTION Referring to FIG. 1, reference character 1 indicates a U-shaped base plate having a mounting portion 2, a vertical portion 3, and a horizontal portion 4 which supports a switch panel 5. The switch panel 5 supports a pair of stationary contact bars 6 carrying stationary contacts 7 and being attached to terminals 8 for attachment of external lead wires. The terminal panel 6 in the space between the ends of the stationary contact bars is formed with a slot 9 which receives a slide type of switch operator 10. This switch operator extends parallel with the vertical portion 3 of the bracket 1 and is guided at its lower end by a guide 11 attached to portion 3 of bracket 1. As shown in FIG. 1, the operator 10 is formed with a slot 12 which fits over a reduced portion I3 of the guide. The slot 9 and guide 11 permit free up and down motion of the slide but prevent lateral or side wise motion thereof.

The slide at its upper end carries a movable contact bar 15 carrying movable contact 16. The upper end of the slide is formed with a reduced portion 18 providing a shoulder 19 supporting a leaf spring 20 urging the contact bar 15 upwardly against a pin 21 pressed into the top portion 18 of this slide. This arrangement allows for a rocking or equalizing motion of the movable contact bar on the slide andat the same time provides a rigid non-yielding connection between the slideand the contact bar when the contacts engage.

The slide is formed with a slot 23 defined by opposing characterized camming surfaces 24 and 25. A solenoid operated roller 26 is located in the slot 23. The width of slot 23 is slightly greater than the diameter of the roller to avoid binding. However, it is preferable that the width of the slot be no wider than necessary to provide free action of the roller in the slot.

As shown in FIGS. 4 and 5, the roller 26 is carried on a pin 27 received in a solenoid plunger yoke 28 mounted on plunger 29 of solenoid 30. The yoke 28 is formed with a slot 31 in each of its leg portions which receive the pin 27. Also mounted on the pin 27 are rollers 32 and 33 which rotate on the pin independently of the center roller 26. Preferably the rollers 32 and 33 are pressed on pin 27 providing an assembly that will not come apart in handling.

Mounted on the bracket portion 3 is a stud 35 carrying a pressure lever 36. As shown in FIG. 2 the pressure lever is formed with down turned cars 37 having holes through which the stud 35 passes. This lever is also provided with a birfurcated lever section which straddles the slide 10 as shown in FIG. 3. This lever portion includes one leg 38 which rides on roller 32 and another leg 39 riding the roller 33.

As shown in FIG. 3 the roller 26 rides on a stationary contact surface 40 formed on bracket 41 attached to portion 3 of base number 1. The bracket 41 is secured to base portion 3 by means of a shoulder 42 formed on the stud 35 which also supports the pressure lever 36. The bracket 41 also includes a downwardly depending portion 43 which is secured to base portion 3 by means of a set screw 44. A hole is formed in portion 43 through which the screw 44 passes which is considerably larger than the diameter of the screw. This permits the bracket to be adjusted and then locked in place by the screw. 4

A spring 45 is carried by the stud 35 inside the leg portions 37 of the pressure lever 36. One end of the spring bears upon the end of the pressure lever and the other end bears on the end of the stationary surface bracket 41. It will be apparent that the spring 45. biases the pressure lever clockwise about its pivot putting downward pressure on the rollers 32 and 33 which in i turn put downward pressure on the central roller 26.

OPERATION OF FIG. 1

In FIG. 1 the outline of the solenoid yoke has been omitted for sake of clarity. The parts are shown in the positions assumed when the solenoid is deenergized. At this time the solenoid spring 46 has urged the solenoid plunger 29 to the left which in turn has moved the roller 26 to the left. Its engagement with the upper cam surface 25 on the solenoid slide has lifted this slide to its upper position in which the contacts are separated. At this time the spring 45 applies pressure'through the pressure lever and the rollers to the roller 26 thus urging it downwardly in contact with the stationary surface 40.

When the solenoid is energized, its plunger 29 moves to the right compressing the solenoid spring 46. This through yoke 28 carries the roller assembly to the right and roller 26 riding on the camming surface 24 of the slide causes downward movement of the slide. The initial slope on the camming surface 24 is relatively steep causing a relatively large movement of the slide per increment of movement of the solenoid lever during the portion of the stroke taking up the contact gap. As the contacts approach engagement, the camming surface slope decreases which slows down the movement of the slide and also gives the solenoid a large mechanical advantage at the point of contact engagement. As the contacts engage, the roller 26 rides off the end of the stationary surface 40 and the full force of the spring 45 is available for providing contact pressure holding the contacts in engagement.

When the solenoid is deenergized the opposite action takes place. Roller 26 now moves to the left back onto the stationary surface 40 and bears against the upper camming surface 25 on slide. At the beginning of the out stroke of the solenoid, the roller 26 engages the portion 25 of the camming surface which provides but a small increment of movement of the slide 10 per increment of movement of the solenoid plunger 29. This provides a substantial mechanical advantage to the solenoid in its initial movement for breaking the contacts loose if they should have welded. After the initial break loose movement of the solenoid plunger, the roller 26 engages the steep portion of the camming surface 25 which provides for a large movement of the slide 10 per increment of movement of the solenoid plunger.

From the foregoing it will be apparent that the mechanism disclosed moves the contact bar slide against substantially no force during the movement taking up the contact gap. At this time littlework is required and the solenoid drives the slide through this portion of its stroke in high gear". As the contacts approach engagement, the driving ratio is changed to slow down the contacts at the impact point and also to provide primarily force rather than movement. When the contacts engage, the contact pressure provided by the spring 45 is rolled onto the slide. It is not necessary for the solenoid to develop the contact pressure force by compressing springs. The contact pressure is already there in the preloaded spring 45 and its pressure is simply rolled on or off of the contact bar slide.

It should also be noted that the contact bar 15 is always pressed against the pin 21 on the slide. Thus when the contacts engage there is nothing to yield and allow the contacts to bounce. In order for the contacts to bounce, the inertia of the bounce must be such as to overcome the inertia of the solenoid slide, the roller assembly and the spring lever. The combined inertia of these parts together with the pressure provided by spring 45 is available to oppose the bounce and consequently bounce is very little if any. This elimination of contact bounce makes welding highly unlikely and adds greatly to the useful life of the contacts.

FIGS. 6 AND 7 8 FIG. 6 shows a modified form of the invention in which the variable ratio effect is achieved by compound levers instead of camming.

In this embodiment of the invention the movable contact bar is supported on a slide 50 which passes through the upper wall 51 of an enclosure and which supports the stationary contact bar 6'. The lower end of the slide 50 is bifurcated and straddles a lever 52 which is pivoted at 53 and is biased downwardly by a biasing spring 54. A pin 55 passing through slide 50 and lever 52 attaches these parts together so they move in unison.

A stud 56 is secured to the enclosure and supports a bell crank lever generally indicated as 57. One leg of the lever carries a roller 58 which rides on a curved stationary surface 59 formed on a bracket 60 secured to the enclosure. The curve on the stationary surface 49 is preferably centered about the stud 56. The bellcrank lever 57 is formed with a second leg 61 extending beneath the switch operating lever 52 and engages this lever at point 62 close to its .pivot pin 53. Lever portion 61 is also attached to plunger 63 of solenoid 64 having a return spring 65. The bell crank lever 57 is provided with a slot 66 receiving the pivot pin 56. The slot 66 extends in alignment with the roller 58 and with a tension spring 67 one end of which is attached to the bell crank lever and the other end to a fixed support. It will be apparent that spring 67 serves to pull the lever downwardly causing the roller 58 to ride on the curved stationary surface 59.

When the solenoid 64 is energized, this plunger moves downwardly against the action of return spring 65 and rotates lever 57 clockwise about its pivot 56. The end portion 62 of lever 57 moves downwardly and this allows downward movement of the switch operator lever 52 under the action of spring 54. As point 62 of lever 57 is in proximity to the pivot 53 of the lever 52, the lever 52 moves. rapidly during the initial portion of the down stroke of the solenoid plunger. As the contacts approach engagement the lower end 68 of lever 52 engages arm 61 of lever 57. Lever 52 now slows down due to the change in ratio of the lever arms in action. As the contacts engage, the roller 58 rides of the curved stationary surface 59 onto the upper surface 69 of the end of the switch operator lever 52. The full force of the spring 67 is now applied to the end of lever 52 thus providing substantial contact pressure between the movable and stationary contacts. This condition of the parts is shown in FIG. 7.

When the solenoid 64 is deenergized, its spring 65 rocks the lever 57 counter-clockwise. The initial motion moves the roller 58 from contact with the upper end of the switch operator lever 52. Then lever 57 engages lever 52 at point 68 and starts moving lever 52 upwardly with a slow positive action. At this initial breaking time the lever system provides minimum speed and maximum force on the lever 52 for separating the contacts. After the contacts are disengaged the end 62 of the lever 57 engages lever 52 and causes it to move with rapid action through the remainder of the contact gap.

From the foregoing it will be seen that the invention provides a new type of switch operating mechanism. The invention provides movement against minimum forces through the contact gap. It also provides a substantial force at the point where the contacts engage and no movement is required, As a result the work whether it be an electro-magnet or other type is greatly reduced thus decreasing the size and cost of the switching package.

It will also be apparent that the invention slows down the contact speed at the point of engagement thus reducing the tendency to bounce. In addition the invention opposes the tendency to bounce by the inertia of most of the working parts which substantially eliminates contact bounce and greatly improves contact life.

While preferred. forms of the invention have been shown and described it is obvious that many modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims.

l claim:

1. In a switching mechanism, the combination of, stationary contact means, movable contact means movable from a location spaced from the stationary contact means through a gap into engagement with said stationary contact means, actuator means arranged upon movement thereof in a first direction to move said movable contact means through said gap, preloaded spring means having one portion supported independently of the movable contact means and actuator means, and meansmechanically actuated by said actuator means upon moving of the contact means into engagement for applying force from another portion of the preloaded spring means to the movable contact means in a manner applying contact engagement pressure to said contact means.

2. The combination recited in claim 1 in which the actuator means is constructed and arranged on movement in a second direction to first remove the applied force from the preloaded spring means and then move the movable contact means through said gap.

3. In a switching mechanism, movable contact means, stationary contact means, driven actuator means for selectively causing movement of said movable contact means into engagement with the stationary contact means or away from same providing a gap therebetween, the driven actuator means and movable contact means being constructed and arranged to engage said contact means with a substantially solid nonresilient action between the movable contact means and driven actuator means, power means having a driving actuator means movable in one direction or another, non-linear motion transmitting means between said driving and driven actuator means whereby the driving actuator means actuates the driven actuator means at a predetermined varying rate relative to movement of the power actuated means, preloaded spring means having one portion supported independently of the movable contact means and driven actuator means and, means mechanically actuated by one of said actuator means upon moving of the contact means into engagement for applying force from the preloaded spring means to the movable contact means in a manner applying yieldable contact engagement pressure to said contact means, said non-linear means being arranged to provide a relatively large movement of the driven actuator means per increment of movement of the driving actuator means when the movable contact means is being moved through the gap and a relatively small movement at the point where the contact means engage.

4. The combination recited in claim 3 in which the means for applying force from the preloaded spring means to the movable contact means continuously applies such force to the driving actuator means.

5. The combination recited in claim 3 in which the means for applying force from the preloaded spring means to the movable contact means continuously applies such force to the driving actuator means, said force being applied to the driven actuator means when the contact means are in engagement.

6. in a switching mechanism, movable contact means, stationary contact means, driven actuator means for selectively causing movement of said movable contact means into engagement with the stationary contact means or away from same providing a gap therebetween, the driven actuator means and movable contact means being constructed and arranged to engage said contact means with a substantially solid nonresilient action between the movable contact means and driven actuator means, power means having a driving actuator means movable in one direction or another, camming means between said driving actuator means and driven actuator means, said camming means being characterized to provide a relatively large movement of the driven actuator means per increment of movement of the driving actuator means when the movable contact means is being moved through the gap, and a relatively small movement at the point where the contact means engage, preloaded spring means having one portion supported independently of the movable contact means and driven actuator means and mechanical means actuated by one of the actuator means upon moving of the contact means into engagement for applying force from another portion of the preloaded spring means to the movable contact means in a manner applying yieldable contact engagement pressure to said contact means.

7. The combination recited in claim 6 in which the preloaded spring means applies force to the driven actuator means as the contacts engage.

8. The combination recited in claim 7 in which the actuator means on movement in contact disengaging direction first removes the applied force of the spring loaded means and then moves the movable contact means through the gap.

9. The combination recited in claim 6 including double acting camming surfaces on one actuator means engaged by the other actuator means, providing a positive drive of the driven actuator means in both directions.

10. The combination recited in claim 6 in which the driving actuator means includes roller means, and the driven actuator means includes double acting camming surfaces engaged by the roller means to provide a positive drive of the driven actuator means in both directions.

11. In a switching mechanism, stationary contact means, movable contact means movable from a location spaced from the stationary contact through a gap into engagement with said stationary contact means, actuator means for moving said movable contact means through said gap into engagement with the stationary contact means, and spring loaded means for applying pressure for engagement of said contact means, said spring loaded means including roller means, a track, spring means pressing the roller means against the track, means moving said roller means on said track when the actuator means moves the movable contact means through the gap, and means engaged by the roller means when the contact means engage for applying the pressure on said roller means to the movable contact means.

12. The combination recited in claim 1 l in which the track and means engaged by the roller means have ends adjacent each other, the roller means riding off the end of the track onto the engaged means.

13. In a switching mechanism, the combination of, a switch base of insulating material, a pair of stationary contacts mounting on the base and spaced from each other, a slot in said base between said stationary contacts, a slide actuator extending through said slot, a movable contact bridging bar carried by said slide actuator and extending into engaging relationship with said stationary contacts, said slide actuator having spaced supports arranged to guide the slide actuator and permit movement in a longitudinal direction for engaging the contacts or moving the movable contact bar away from the stationary contacts providing a gap therebetween, said movable contact bar being pivotally connected to said slide actuator in a manner providing a substantially rigid non-yielding action between the slide actuator and bar when both movable contacts engage the stationary contacts, power means having a driving actuator movable in one direction or another, non-linear motion transmitting means between the driving actuator and said slide actuator, said non-linear means being arranged to provide a relatively large movementof the slide actuator per increment of movement of the driving actuator when the movable contact bar is being moved through the gap, and a relatively small movement at the point where the contacts engage, preloaded spring means having one portion supported independently of the slide actuator and movable contact bar and means for applying force from another portion of the preloaded spring means to the slide actuator when the contacts are engaged, in a manner applying yieldable contact engaging pressure to the contacts.

14. The combination recited in claim 13 in which the non-linear motion transmitting means includes a camming surface on the slide actuator and roller means moved by the driving actuator and riding on said camming surface the means for applying force from the other portion of the spring means to the slide actuator acting through said roller means.

15. In a switching mechanism, movable contact means, stationary contact means, driven actuator means for selectively causing movement of said movable contact means into engagement with the stationary contact means or away from said stationary contact means providing a gap therebetween, power means having a driving actuator means movable in one direction or another, said driven actuator means and driving actuator means being levers having spaced pivot points and arranged to contact at different points of engagement between said pivot points as the driving actuator means drives the driven actuator means, thereby changing the rate of movement of the driven actuator means relative to that of the driving actuator means, the levers being constructed and arranged to provide a relatively large movement of the driven actuator means per increment of movement of the driving actuator means when the movable contact means is being moved through the gap and a relatively small movement at the point where the contacts engage.

16. In a switching mechanism, movable contact means, stationary contact means, driven actuator means for selectively causing movement of said movable contact means into engagement with the stationary contact means or away from same providing a gap therebetween, the driven actuator means and movable contact means being constructed and arranged to engage said contact means with a substantially solid nonresilient action between the movable contact means and driven actuator means, power means having a driving actuator means movable in one direction or another, said driving actuator means including roller means, cam surface means on the driven actuator means arranged to be engaged by the roller means in a manner moving the movable contact means toward engagement with the stationary contact means when the driving actuator means moves in one direction, preloaded spring means arranged to apply pressure constantly to said roller means and toward said cam surface means, said preloaded spring means acting through said roller means to apply yieldable contact engaging pressure to the contact means when said contact,

means are engaged.

17. The combination recited in claim 16 including a track for the roller means arranged to hold the same for movement by the pre-loaded spring means when the movable contact means is being moved through the gap, said-track being arranged to release the roller means when the contact means engage, thus applying the force of the spring means through the driven actuator means to the movable contact means.

18. In a switching mechanism, movable contact means, stationary contact means, driven actuator means for selectively causing movement of said movable contact means intoengagement with the stationary contact means or away from same providing a gap therebetween, the driven actuator means and movable contact means being constructed and arranged to engage said contact means with a substantially solid nonresilient action between the movable contact means and driven actuator means, power means having a driving actuator means movable in one direction or another, motion transmitting means between said driving and driven actuator means whereby the driving actuator means actuates the driven actuating means, preloaded spring means having one portion supported independently of the movable contact means and one of the actuator'means, said preloaded spring means being arranged to apply pressure continuously to the other of said actuator means, and means mechanically actuated by one of the actuator means for applying force from the preloaded spring means to the movable contact means when the contacts are engaged. 

1. In a switching mechanism, the combination of, stationary contact means, movable contact means movable from a location spaced from the stationary contact means through a gap into engagement with said stationary contact means, actuator means arranged upon movement thereof in a first direction to move said movable contact means through said gap, preloaded spring means having one portion supported independently of the movable contact means and actuator means, and means mechanically actuated by said actuator means upon moving of the contact means into engagement for applying force from another portion of the preloaded spring means to the movable contact means in a manner applying contact engagement pressure to said contact means.
 2. The combination recited in claim 1 in which the actuator means is constructed and arranged on movement in a second direction to first remove the applied force from the preloaded spring means and then move the movable contact means through said gap.
 3. In a switching mechanism, movable contact means, stationary contact means, driven actuator means for selectively causing movement of said movable contact means into engagement with the stationary contact means or away from same providing a gap therebetween, the driven acTuator means and movable contact means being constructed and arranged to engage said contact means with a substantially solid non-resilient action between the movable contact means and driven actuator means, power means having a driving actuator means movable in one direction or another, non-linear motion transmitting means between said driving and driven actuator means whereby the driving actuator means actuates the driven actuator means at a predetermined varying rate relative to movement of the power actuated means, preloaded spring means having one portion supported independently of the movable contact means and driven actuator means and, means mechanically actuated by one of said actuator means upon moving of the contact means into engagement for applying force from the preloaded spring means to the movable contact means in a manner applying yieldable contact engagement pressure to said contact means, said non-linear means being arranged to provide a relatively large movement of the driven actuator means per increment of movement of the driving actuator means when the movable contact means is being moved through the gap and a relatively small movement at the point where the contact means engage.
 4. The combination recited in claim 3 in which the means for applying force from the preloaded spring means to the movable contact means continuously applies such force to the driving actuator means.
 5. The combination recited in claim 3 in which the means for applying force from the preloaded spring means to the movable contact means continuously applies such force to the driving actuator means, said force being applied to the driven actuator means when the contact means are in engagement.
 6. In a switching mechanism, movable contact means, stationary contact means, driven actuator means for selectively causing movement of said movable contact means into engagement with the stationary contact means or away from same providing a gap therebetween, the driven actuator means and movable contact means being constructed and arranged to engage said contact means with a substantially solid non-resilient action between the movable contact means and driven actuator means, power means having a driving actuator means movable in one direction or another, camming means between said driving actuator means and driven actuator means, said camming means being characterized to provide a relatively large movement of the driven actuator means per increment of movement of the driving actuator means when the movable contact means is being moved through the gap, and a relatively small movement at the point where the contact means engage, preloaded spring means having one portion supported independently of the movable contact means and driven actuator means and mechanical means actuated by one of the actuator means upon moving of the contact means into engagement for applying force from another portion of the preloaded spring means to the movable contact means in a manner applying yieldable contact engagement pressure to said contact means.
 7. The combination recited in claim 6 in which the preloaded spring means applies force to the driven actuator means as the contacts engage.
 8. The combination recited in claim 7 in which the actuator means on movement in contact disengaging direction first removes the applied force of the spring loaded means and then moves the movable contact means through the gap.
 9. The combination recited in claim 6 including double acting camming surfaces on one actuator means engaged by the other actuator means, providing a positive drive of the driven actuator means in both directions.
 10. The combination recited in claim 6 in which the driving actuator means includes roller means, and the driven actuator means includes double acting camming surfaces engaged by the roller means to provide a positive drive of the driven actuator means in both directions.
 11. In a switching mechanism, stationary contact means, movable contact means movable From a location spaced from the stationary contact through a gap into engagement with said stationary contact means, actuator means for moving said movable contact means through said gap into engagement with the stationary contact means, and spring loaded means for applying pressure for engagement of said contact means, said spring loaded means including roller means, a track, spring means pressing the roller means against the track, means moving said roller means on said track when the actuator means moves the movable contact means through the gap, and means engaged by the roller means when the contact means engage for applying the pressure on said roller means to the movable contact means.
 12. The combination recited in claim 11 in which the track and means engaged by the roller means have ends adjacent each other, the roller means riding off the end of the track onto the engaged means.
 13. In a switching mechanism, the combination of, a switch base of insulating material, a pair of stationary contacts mounting on the base and spaced from each other, a slot in said base between said stationary contacts, a slide actuator extending through said slot, a movable contact bridging bar carried by said slide actuator and extending into engaging relationship with said stationary contacts, said slide actuator having spaced supports arranged to guide the slide actuator and permit movement in a longitudinal direction for engaging the contacts or moving the movable contact bar away from the stationary contacts providing a gap therebetween, said movable contact bar being pivotally connected to said slide actuator in a manner providing a substantially rigid non-yielding action between the slide actuator and bar when both movable contacts engage the stationary contacts, power means having a driving actuator movable in one direction or another, non-linear motion transmitting means between the driving actuator and said slide actuator, said non-linear means being arranged to provide a relatively large movement of the slide actuator per increment of movement of the driving actuator when the movable contact bar is being moved through the gap, and a relatively small movement at the point where the contacts engage, preloaded spring means having one portion supported independently of the slide actuator and movable contact bar and means for applying force from another portion of the preloaded spring means to the slide actuator when the contacts are engaged, in a manner applying yieldable contact engaging pressure to the contacts.
 14. The combination recited in claim 13 in which the non-linear motion transmitting means includes a camming surface on the slide actuator and roller means moved by the driving actuator and riding on said camming surface the means for applying force from the other portion of the spring means to the slide actuator acting through said roller means.
 15. In a switching mechanism, movable contact means, stationary contact means, driven actuator means for selectively causing movement of said movable contact means into engagement with the stationary contact means or away from said stationary contact means providing a gap therebetween, power means having a driving actuator means movable in one direction or another, said driven actuator means and driving actuator means being levers having spaced pivot points and arranged to contact at different points of engagement between said pivot points as the driving actuator means drives the driven actuator means, thereby changing the rate of movement of the driven actuator means relative to that of the driving actuator means, the levers being constructed and arranged to provide a relatively large movement of the driven actuator means per increment of movement of the driving actuator means when the movable contact means is being moved through the gap and a relatively small movement at the point where the contacts engage.
 16. In a switching mechanism, movable contact means, stationary contact means, driven actuator means for seLectively causing movement of said movable contact means into engagement with the stationary contact means or away from same providing a gap therebetween, the driven actuator means and movable contact means being constructed and arranged to engage said contact means with a substantially solid non-resilient action between the movable contact means and driven actuator means, power means having a driving actuator means movable in one direction or another, said driving actuator means including roller means, cam surface means on the driven actuator means arranged to be engaged by the roller means in a manner moving the movable contact means toward engagement with the stationary contact means when the driving actuator means moves in one direction, preloaded spring means arranged to apply pressure constantly to said roller means and toward said cam surface means, said preloaded spring means acting through said roller means to apply yieldable contact engaging pressure to the contact means when said contact means are engaged.
 17. The combination recited in claim 16 including a track for the roller means arranged to hold the same for movement by the pre-loaded spring means when the movable contact means is being moved through the gap, said track being arranged to release the roller means when the contact means engage, thus applying the force of the spring means through the driven actuator means to the movable contact means.
 18. In a switching mechanism, movable contact means, stationary contact means, driven actuator means for selectively causing movement of said movable contact means into engagement with the stationary contact means or away from same providing a gap therebetween, the driven actuator means and movable contact means being constructed and arranged to engage said contact means with a substantially solid non-resilient action between the movable contact means and driven actuator means, power means having a driving actuator means movable in one direction or another, motion transmitting means between said driving and driven actuator means whereby the driving actuator means actuates the driven actuating means, preloaded spring means having one portion supported independently of the movable contact means and one of the actuator means, said preloaded spring means being arranged to apply pressure continuously to the other of said actuator means, and means mechanically actuated by one of the actuator means for applying force from the preloaded spring means to the movable contact means when the contacts are engaged. 